Manual transmissions for use in automotive vehicles typically include a main shaft and a countershaft upon which torque transmitting gears are mounted for establishing and interrupting discreet torque transmitting paths. They typically include synchronizer clutches having clutch sleeves that are adjusted to effect driving torque distribution through the gearing. The synchronizers are adjusted by means of a gear shift mechanism including shift forks carried on shift rails. Selection by the driver of a shift rail for a particular ratio is accomplished by adjusting a manually controlled shift lever in one shift plane and shifting the selected shift rail as the shift lever is adjusted by the driver in a different shift plane.
In a so-called shift-by-wire manual transmission, the mechanical shift mechanism is replaced by servo operators that effect shifting movement of the shift rails. The servo operators are controlled by opening and closing ratio controlling switches in a control panel. Such shift-by-wire transmissions require sensors for detecting a defective circuit in any of the switches which would interfere with a ratio controlling sequence or ratio range selection.